Mashl is an essential transcription factor in neural development throughout multiple regions of the central and peripheral nervous systems. Mashl expression is tightly regulated; it is expressed in proliferating neural stem cells and is downregulated as the cells become post- mitotic and mature into neurons. Synthesizing results from multiple investigators on Mashl expression and function, we hypothesize that 1) Mashl expression is controlled by signals instructing stem cells to begin the differentiation program, 2) the specificity of function for a particular bHLH involves interacting factors, and 3) in a neural progenitor cell, Mashl functions in transcriptional control of some but not all pathways required for neuronal differentiation. Experiments here will address these hypotheses, and identify specific molecular components upstream and downstream of this essential neural differentiation factor. We will identify! transcription factors that bind the Mashl enhancer to control Mashl expression in the spinal neural tube. We will identify structural domains in Mashl required for specific functions in neurogenesis and screen for interacting factors that modulate these functions. And finally, we will identify the specific: regulatory pathways during neuronal differentiation controlled by Mashl by analysis of gene expression profiles in multiple loss- and gain-of-function paradigms. Success in this research program will increase our understanding of molecular mechanisms! involved in neural precursor proliferation, differentiation, and specification. This! understanding is important for future therapeutic strategies in treating neurological disorders! involving neuronal cell death such as Parkinson's Disease, and in regenerative strategies fon treatment of brain and spinal cord damage. j . j 3ERFORMANCE SITE(S) (organization, city, state) University of Texas Southwestern Medical Center, Dallas, Texas KEY PERSONNEL. See instructions on Page 11. Usecontinuationpages as neededto provide the required information in the format shown below. Name Organization Role on Project Johnson, Jane E. UT Southwestern PI Henke, R. Michael UT Southwestern Postdoc Liu, Ying UT Southwestern Postdoc Zhao, Yingming UT Southwestern Collaborator PHS 398 (Rev.4/98) Page 2 BB Number pages consecutively at the bottom throughout the application. Do not use suffixes such as 3a, 3b. CC Princip^^estigator/Program Director (Last, first, middle): Jfctne E. Johnson Type the name of the principal investigator/program director at the top of each printed page and each continuation page. (For type specifications, see instructions on page 6.) RESEARCH GRANT TABLE OF CONTENTS Page Numbers Face Page 1 Description,